1. Field of the Invention
The present invention relates to a solid-state imaging device, particularly, a solid-state imaging device, for example, a MOS image sensor in which a photoelectric conversion portion and a pixel transistor are included in a pixel. In addition, the present invention relates to a camera module including such a solid-state imaging device.
2. Description of the Related Art
Solid-state imaging devices can be roughly classified into charge transfer solid-state imaging devices typified by CCD image sensors and amplified solid-state imaging devices typified by CMOS image sensors. In comparison with the CMOS image sensor, the CCD image sensor may need a power supply voltage higher than that of the CMOS image sensor, because the CCD image sensor may require a high driving voltage for the transfer of a signal electric charge.
Therefore, CMOS image sensors having advantages over the CCD image sensors in terms of lower power source supply, power consumption, and the like, compared with those of the CCD image sensors, are mounted as the solid-state imaging device on mobile devices, such as camera cell phones and personal digital assistants (PDFs), which have been used in large numbers in recent years.
The solid-state imaging device used in any mobile device or the like has a reduced area per pixel along with a miniaturization and a high-resolution. In addition, the area of a photodiode that is to be provided as a photoelectric conversion portion is reduced along with a decrease in the area of the pixel. Thus, it may result in a decrease in sensitivity or the like. Therefore, for example, for allowing an user to take a bright image of a dark subject, a solid-state imaging device having a unit pixel matrix including pixels on which infrared light (IR) is incident and other color pixels with optical inner filter layers for blocking infrared light (or inner-layer IR cut filter layers) has been known in the art (see Japanese Unexamined Patent Application Publication No. 2006-190958).
FIG. 1 illustrates a CMOS image sensor without a filter layer for blocking infrared light, while FIG. 2 illustrates a CMOS image sensor provided with a filter layer for blocking infrared light. In FIGS. 1 and 2, a pixel is schematically represented only by a photodiode PD, while a pixel transistor is omitted for making the configuration of the CMOS image sensor clearly understandable.
The CMOS image sensor 1, as illustrated in FIG. 1, includes an imaging area formed of a plurality of pixels provided in a two-dimensional array. Each of the pixels has a photodiode (PD) 3 as a photoelectric conversion portion and a plurality of pixel transistors (MOS transistors, not shown) on the principal surface of a semiconductor substrate 2. A plurality of wiring layers 6 with a plurality of layered lines 5 through an insulating interlayer 4 is formed on the principal surface of the pixel-formed semiconductor substrate 2. Furthermore, a color filter 7 and an on-chip micro lens 8 are formed above the plurality of wiring layers 6 through a planarizing layer (not shown).
The CMOS image sensor 11, as illustrated in FIG. 2, includes an imaging area formed of a plurality of pixels provided in a two-dimensional array. Each of the pixels has a photodiode (PD) 3 as a photoelectric conversion portion and a plurality of pixel transistors (MOS transistors, not shown) on the principal surface of a semiconductor substrate 2. A plurality of wiring layers 6 with a plurality of layered lines 5 through an insulating interlayer 4 is formed on the principal surface of the pixel-formed semiconductor substrate 2. Furthermore, an optical inner filter layer (inner-layer IR cut filter layer) 12 is formed above the plurality of wiring layers 6 for a pixel on which the incidence of infrared light should be blocked. In other words, the optical inner filter layer 12 is formed above each of the pixels of red (R), green (G), and blue (B), but no optical inner filter layer 12 is formed above one pixel (that is, the IR pixel). A buried layer 13 is formed on an area on which no optical inner filter layer 12 is formed, and a color filter 7 and an on-chip micro lens 8 are then formed through a planarizing layer (not shown). Here, a unit pixel matrix includes four pixels, that is, the R, G, and B pixels and the IR pixel. The color filter for the IR pixel is formed of a filter transmitting visible light and infrared light.
The CMOS image sensor 11 includes the IR pixel which positively uses infrared light, so that the sensitivity thereof can be enhanced to allow an user to take a bright image with suitable color tone, for example, when the user wishes to take a bright image of a dark subject.